Pager pipe (like git)

maybe-pager.go

package main
// From
// http://stackoverflow.com/questions/21738674/how-do-i-print-a-buffer-to-stdout-piped-through-a-pager
// http://rosettacode.org/wiki/Terminal_control/Dimensions

import (
	"bufio"
	"io"
	"os"
	"os/exec"

	"bytes"
	"code.google.com/p/go.crypto/ssh/terminal"
	"log"
)

func page(b bytes.Buffer) {
	pager := os.Getenv("PAGER")
	if pager == "" {
		pager = "pager"
	}
	cmd := exec.Command(pager)

	r, stdin := io.Pipe()

	cmd.Stdin = r
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	c := make(chan struct{})
	go func() {
		defer close(c)
		cmd.Run()
	}()

	b.WriteTo(stdin)
	io.Copy(stdin, os.Stdin)

	stdin.Close()

	<-c
}

func main() {
	w, h, err := terminal.GetSize(int(os.Stdout.Fd()))
	if nil != err {
		log.Fatal(err)
	}

	var b bytes.Buffer
	scanner := bufio.NewScanner(os.Stdin)
	height := 0
	for scanner.Scan() {
		line := scanner.Text()
		add := len(line) / w
		if len(line)%w > 0 {
			add++
		}
		b.WriteString(line + "\n")
		height += add

		if height > h {
			page(b)
			return
		}
	}

	b.WriteTo(os.Stdout)
}